9 JSTS Vol. 27, No. 2 A Study of Thermal Protection System for HTV-R Reentry (6) POWER REQUIREMENT The advanced HTV-R type is designed for reduced consumption of electrical power. A vehicle’s Yasuhide WATANABE1) power requirement determines the area of the solar panel and radiator size, and this affects the Kazuhisa FUJITA2), Toshiyuki SUZUKI2), vehicle’s configuration. Data of the current HTV's power consumption is useful to estimate the power Toshio OGASAWARA2), Takuya AOKI2), Yuichi ISHIDA2), consumption of the advanced type, for they share almost the same orbital trajectory. The heaters in the Keisuke FUJII2), Masahito MIZUNO2) and Tetsuya YAMADA3) HTV’s cargo transport vehicle consume a large amount of power because the large surface area of the , carrier radiates a lot of heat. They will be improved in advanced HTV-R. Table 2 is a summary of the estimated power consumption. 1) Japan Aerospace Exploration Agency (JAXA), 2-1-1, Sengen, Tsukuba, Ibaraki, 305-8505 Japan 2)Japan Aerospace Exploration Agency (JAXA), Chofu, Tokyo, 182-8522 Japan Table 2. Power Consumption Estimation (w) 3)Japan Aerospace Exploration Agency (JAXA), Sagamihara, Kanagawa, 252-5210 Japan HTV Advanced Note Heater (in PLC) 778.3 258.8 Relative to surface Component (in PLC) 153.5 153.5 TEL / FAX: +81-29-868-5000 / +81-29-868-2966 Heater (in UPLC) 53.1 26.6 E-mail: [email protected] Component (in UPLC) 29.5 14.8 Relative to volume Heater (in Avio. Module) 234.7 0 Installed in PLC Avionics 793.8 396.9 Power saving ABSTRACT Heater (in Prop. Module) 289.8 144.9 Relative to surface HTV-R aims to return payloads from the ISS to the Earth in the near future mission. This system Component (in Prop. Module) 94.9 94.9 contains new technologies for reentry, especially a thermal protection systemwith low-density ablator. Total 2,427.6 1,090.4 This paper describes technical issues and basic research of the thermal protection system for HTV-R to realize Japanese return missions from the ISS. 5. CONCLUSION JAXA continues investigations and tradeoff studies for the development of the HTV-R program. 1. INTRODUCTION A detailed development plan is necessary to estimate the total budget for the program’s completion The HTV-R concept is the Japanese unmanned reentry vehicle from the International Space Station and to determine JAXA’s future direction. (Figure 1). This concept is currently under study and aims to launch by 2020. The size of the reentry The start date of the program and the first flight target date is unknown, but initiation of JAXA’s capsule is 3 m in height and approximately 4 m in maximum diameter, to meet the requirements of the HTV-R development will mark a solid step towards the future development of manned spaceships. future Japanese manned space capsule. The HTV-R’s capsule receives a large heat load when passing The first HTV-R flight and HRV re-entry will represent a major milestone in Japanese human space through the Earth atmosphere during reentry flight. The HRV must be protected against the heat load activities. of rising surface temperature of approximately 2000° Celsius. This report presents a summary of technical issues and research activities on the thermal protection system of the HTV-R concept. REFERENCES [1] Suzuki, Y., Imada, I.: Concept and Technology of HTV-R: An Advanced Type of H-II Transfer Vehicle, ists28 (2011), [2] Anon.: Apollo Operations Handbook Block II Spacecraft, SM2A-03-BK-II-(1). [3] Anon.: NASA's Exploration Systems Architecture Study, NASA-TM-2005-214062. [4] Anon.: DragonLabTM Fast track to flight, SpaceX [5] Rex D. Hall, David J. Shayler : Soyuz – A Universal Spacecraft, Springer Praxis Publishing Figure 1. HTV-R concept ⓒ Japanese Rocket Society 10 2. HTV-R CONCEPT The present HTV mission is to transport supplies to the International Space Station (ISS). However, this space vehicle can only effectively travel one way: to the ISS, and so it does not have the ability to transport cargo from the ISS to the ground. Thus, the present recovery methods of Japanese experimental materials depend on the Russian Soyuz and American Dragon capsules. Reentry and recovery technology from space will become more important in the near future. The target of manned flights to the Moon and Mars is expected to increase competition in life science technology development from ISS experiments by 2020. This status around the ISS lends weight to the necessity of reentry technology. Research for the HTV-R Japanese vehicle concept for the aforementioned purpose began in 2010. The ‘-R’ in HTV-R stands for “return” because the vehicle has a reentry capsule for return travel from the ISS to Earth. This reentry capsule is called “HRV”. The HRV needs special technology for reentry especially a thermal protection system to lower the heat load during atmospheric flight. (Figure 2) Figure 2. HRV reentry(Image) 3. LOW-DENSITY ABLATOR The entire surface of the HRV capsule must be covered with a thermal protection system (TPS) for protection from large heat loads during the reentry flight. The capsule needs a large heat shield of 4.2 m in diameter, especially at the front where it faces the direction of the flight. The heat shield’s weight must be trimmed to a feasible extent in order to increase the capsule’s payload mass. TPS weight saving is also required for manned capsules. CFRP is the conventional ablative TPS material used for Japanese USERS and HAYABUSA reentry capsules. This material is proven, but it is too heavy. Thus, a new lightweight ablative TPS must be developed for the HRV. There are two technical issues for TPS development. The first is the development of a low-density ablative material, and the second is the design of a large TPS made of low-density ablator. The TPS should consist of individual ablator segments based on the initial conceptual design of the HRV TPS. Research for low-density ablator has been conducted for some years in Japan. However, only small samples of approximately 4cm in diameter were produced in basic performance tests in laboratories, and thus there is a lack of experience in large segment low-density ablator production. The first issue of the research was to investigate the possibility for producing large segments of low-density ablator while avoiding large variations in density and heat resistance performance. A flat panel of 50 square cm and 5 cm width was made in 2011. JAXA collaborated with two Japanese companies for this study. The result was the construction of a low-density ablator segment without 11 JSTS Vol. 27, No. 2 varying density and heat resistance performance. An arc test of low-density ablator is shown in Figure 2. HTV-R CONCEPT 3. This study was the first step of HTV-R TPS development. The present HTV mission is to transport supplies to the International Space Station (ISS). However, this space vehicle can only effectively travel one way: to the ISS, and so it does not have the ability to transport cargo from the ISS to the ground. Thus, the present recovery methods of Japanese experimental materials depend on the Russian Soyuz and American Dragon capsules. Reentry and recovery technology from space will become more important in the near future. The target of manned flights to the Moon and Mars is expected to increase competition in life science technology development from ISS experiments by 2020. This status around the ISS lends weight to the necessity of reentry technology. Research for the HTV-R Japanese vehicle concept for the aforementioned purpose began in 2010. The ‘-R’ in HTV-R stands for “return” because the vehicle has a reentry capsule for return travel from the ISS to Earth. This reentry capsule is called “HRV”. The HRV needs special technology for reentry especially a thermal protection system to lower the heat load during atmospheric flight. (Figure 2) Figure 3. Arc test of JAXA low-density ablator in JAXA Chofu Aerospace Center 4. THERMAL PROTECTION SYSTEM CONSTRUCTION A block construction method using segments of low-density ablator panel is required for the front panel of the HRV TPS (4.2 m diameter) as previously mentioned. A single piece construction method is also available, and both methods have merits and demerits. The latter method requires a new large production facility. The former method’s development cost will be lower if the segments are made in an existing facility, and segments will be easy to repair and change when damaged. However, the block construction method has some technical issues with segment design. The primary one is to Figure 2. HRV reentry(Image) prevent damage to each segment caused by heat expansion during reentry flight. Gap filler between low–density ablator segments was necessary. Consequently, JAXA and collaborating research companies started a gap filler study in 2012. 3. LOW-DENSITY ABLATOR The entire surface of the HRV capsule must be covered with a thermal protection system (TPS) for protection from large heat loads during the reentry flight. The capsule needs a large heat shield of 4.2 5. GAP FILLER DESIGN AND SELECTION m in diameter, especially at the front where it faces the direction of the flight. The heat shield’s Heating rate in the stagnation point on HRV front TPS during reentry flight was calculated using weight must be trimmed to a feasible extent in order to increase the capsule’s payload mass. TPS the Detra-Kemp-Riddell formula [1] (Figure 4). Calculations were made for reentry angle of -1.2 to - weight saving is also required for manned capsules.